There is a photo mosaic given as a technique of generating a single large image by arranging a plurality of small images (such as photos). FIG. 43 is a diagram representing an example of the photo mosaic. The photo mosaic gets a person 501 who views from a remote place to visually recognize a sheet of large image 505 and enables a person 502 who views at close range to visually recognize a plurality of images 511, 512, 513 and 514 which form the sheet of large image 505. This type of photo mosaic technology will hereinafter be simply referred to as the mosaic technology, and the image 505 generated by the photo mosaic technology is simply termed a mosaic image. Further, the images (e.g., the image 511 etc) forming this mosaic image are expressed as material images, and the image serving as a basis of the mosaic image is referred to as a target image.
A variety of tools for generating the mosaic image such as this are provided on the Internet etc at the present. This type of conventional mosaic image creating tool generates the mosaic image by using roughly two techniques given as below in a way that makes a user register one single target image and a plurality of material images.
The first technique is that the target image is segmented into a predetermined number of blocks, some material image close to tones and shapes of the respective blocks are extracted from within the plurality of material image, and the extracted material images are placed on the individual blocks.
The second technique is that the target image is converted into a semi-transparent image, the plurality of material images is placed in a mosaic-like configuration, and the semi-transparent target image is superposed on the plurality of material images.
These conventional techniques are disclosed in the following documents of the conventional arts. Further, a system is proposed (refer to Patent document 4), which generates the mosaic image through operations on a multiplicity of user terminals such as mobile terminals by use of these conventional techniques.    [Patent document 1] Japanese Patent Laid-Open Publication No. 2005-100120    [Patent document 2] Japanese Patent Laid-Open Publication No. H11-341264    [Patent document 3] Japanese Patent Laid-Open Publication No. 2000-306083    [Patent document 4] Japanese Patent Laid-Open Publication No. 2004-30076